Method and system for applying wireless geolocation technology

ABSTRACT

A system and method for determining the positioning of mobile-appliance location determining sensors in a mobile-appliance communications network by estimating the positioning accuracy of the sensors.

RELATED APPLICATIONS

This application is a continuation of and claims benefit of U.S.nonprovisional application Ser. No. 10/046,284, titled “METHOD ANDSYSTEM FOR APPLYING WIRELESS GEOLOCATTON TECHNOLOGY” filed Jan. 16,2002, which claims the benefit of U.S. Provisional Patent ApplicationNo. 60/261,264 filed Jan. 16, 2001.

The present application is related to the following co-pending andcommonly assigned U.S. Patent Applications having inventors in commonwith the present application: application Ser. No. 09/971,680 entitled“System and Method for Geolocating a Wireless Mobile Unit from a SingleBase Station Using Repeatable Ambiguous Measurements”, filed Oct. 9,2001; Application Serial No. (unassigned) entitled “System and Methodfor Analog Cellular Radio Geolocation” filed Dec. 11, 2001; andapplication Ser. No. 10/004,449 entitled “Pseudolite Positioning Systemand Method” filed Dec. 6, 2001 claiming priority of U.S. ProvisionalPatent Application Ser. No. 60/254,134 entitled “Pseudolite PositioningSystem and Method” filed Dec. 11, 2000. The disclosures of theabove-referenced applications are hereby incorporated herein byreference.

BACKGROUND OF THE INVENTION

Applicant's disclosure is directed to the selection and positioning ofmobile-appliance location determining sensors in a wirelesscommunication network. The disclosure assists in the pre-installationdesign of a mobile-appliance location determining system which utilizesa network infrastructure overlay location approach (as opposed totechniques where the location is determined with modifications to themobile-appliance) where equipment is installed within the wirelessnetwork base stations and/or switching centers to determine themobile-appliance location.

The use of wireless communication devices such as telephones, pagers,personal digital assistants, laptop computers, etc., hereinafterreferred to collectively as “mobile-appliances”, has become prevalent intoday's society. Recently, at the urging of public safety groups, thegovernment has begun to require that the providers of mobile-appliancecommunication services geolocate, or determine the geographic position,of the mobile-appliance in certain circumstances. For example, theFederal Communication Commission (FCC) has issued a geolocation mandatefor providers of cellular telephone communication services in order togeolocate a cellular telephone used to make a 911 emergency telephonecall. An accuracy standard (FCC 94-102 E911) has been established by theFCC, which the geolocation systems must meet. Accordingly, the providersof cellular telephone services are interested in location determiningsystems which meet the accuracy standard at the minimum cost.

In addition to E911 emergency related issues, cellulartelecommunications providers are developing location-enabled servicesfor their subscribers including roadside assistance, turn-by turndriving directions, concierge services, location-specific billing ratesand location-specific advertising.

There are two major approaches to determining the location of amobile-appliance. One approach is appliance based and requiresmodification to the conventional mobile-appliance so that themobile-appliance is capable of determining its own location, e.g.,through the use of GPS or some other location system. The other approachis network based and requires modifications to the communication networkso that location sensors can determine the location of the mobileappliance based on the communication signals transmitted between themobile-appliance and the network. Applicant's disclosure is directed tothe selection and placement of mobile-appliance location determiningsensors through the network in order to locate a mobile-appliance.

There are presently a number of techniques available to locate mobileappliances. These include time difference of arrival (TDOA), angle ofarrival (AOA), radio fingerprinting, reverse link power measurements,and collateral data matching (i.e., map or other features useful inestimating location). Each of these techniques has associated with it atheoretical and practical location accuracy, and an associated cost toimplement. The techniques vary widely in their performance as a functionof the radio frequency (RF) propagation environment, base stationgeometry and wireless air interface. For each of the techniques, thereexists many implementation variants and permutations. For example, TDOAcan be implemented using two or four RF channels to measure time ofarrival, and can include spatial filtering techniques to enhanceperformance in certain RF environments. Each of these locationcapabilities has associated with it a different cost, with costgenerally increasing for increased accuracy performance.

A conventional technique for deploying location determining sensors hasbeen to co-locate the sensors with each of the base stations in acommunication network in order to process the communication signalsreceived at the base station. The location determining accuracy providedby such a deployment is then checked by randomly traveling to variousgeographic locations within the coverage area of the communication areawith an independent location determining equipment, i.e., GPS, andcomparing the independent location determination from GPS with thelocation determined from the location determining sensors at the basestations. If the location accuracy of the system is not sufficient,additional location determining sensors can be added apart from the basestations, or the sensors can be replaced with more capable sensors toimprove the accuracy of the system. This method of installing andmeasuring the accuracy of the sensors is labor intensive and expensive.

Other employment techniques have positioned the location determiningsensors at selected base stations and added additional sensors on an adhoc basis as the accuracy verification using GPS or other independentmeans identified areas having substandard location determiningaccuracies.

Thus, the overall cost and performance of the location determiningsystem is largely driven by the number of location determining sensorsinstalled, as well as the types of sensors installed. It is for thisreason that a detailed planning system and method is critical to designa location determining system for performance and cost effectiveness.

Accordingly, it is an object of the present disclosure to provide anovel system and method for determining the position of locationdetermining sensors in a communication system.

It is another object of the present disclosure to provide a novel systemand method for selecting location determining sensors having variouscapabilities in order to meet a predetermined accuracy standard at theleast cost.

It is a further object of the present disclosure to provide a novelsystem and method of positioning location determining sensors based onestimated accuracies without the necessity of actually measuringcommunication signals.

It is yet another object of the present disclosure to provide a novelsystem and method of location determining sensors having variouscapabilities to address the varied signal propagation and sitegeometries in the communication coverage area.

It is still another object of the present disclosure to provide a novelsystem and method for modeling the transmit power of a mobile-appliance.

It is yet still another object of the present disclosure to provide anovel system and method of estimating the TDOA, AOA or collateral datamatching error for a location determining system.

It is still another object of the present disclosure to provide a novelsystem and method of presenting the accuracy results of a locationdetermining system as accuracy contour lines overlaid on a geographicmap.

These and many other objects and advantages of the present inventionwill be readily apparent to one skilled in the art to which thedisclosure pertains from a perusal of the claims, the appended drawings,and the following detailed description of the preferred embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a pictorial representation of a conventional mobile-appliancecommunication system.

FIG. 2 is a flow chart of a method of determining the position ofmobile-appliance location determining sensors in the conventionalmobile-appliance communication system of FIG. 1.

FIG. 3 is a graphical illustration of the location determiningcapabilities of the present disclosure which overcome the environmentalchallenges in a typical communication coverage area.

FIG. 4 is a geographical plot of the accuracy estimations as contourlines for a location system utilizing the method of FIG. 2.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 shows a conventional mobile-appliance communication system havingbase stations 10 for communicating with a mobile-appliance 20. Each basestation 10 contains signal processing equipment and an antenna fortransmitting to and receiving signals from the mobile appliance as wellas other base stations and centrally located control and processingstations (not shown). A mobile-appliance location determining sensor 30may be positioned at some or all of the base stations 10 to determinethe location of a mobile-appliance within the signal coverage area ofthe communication system. The antenna may be a multi-element antenna.The signal reception area of a base station may be divided into sectorsof various orientations depending on the type of antenna configurationand signal processing equipment. The mobile-appliance communicationsystem is designed so that the mobile-appliance preferably has thecapability to communicate with at least one base station while in thecoverage area.

The transmit power level of the mobile-appliance may be controlled by apower management architecture to ensure that the mobile-appliancetransmits at a sufficient power level to be received by at least onebase station, but not high enough to be received at other base stations.Such a power management architecture allows more than onemobile-appliance in the coverage area to use the same frequencysimultaneously while avoiding cross interference.

The capability of the base stations to receive signals from themobile-appliance is based on a number of factors such as the geographiclocation of the base station with respect to the location of themobile-appliance, the height of the antenna, the number of sectors, theorientation of the sectors, the power management architecture and theantenna characteristics.

The propagation of the communication signals in the coverage area isaffected by such factors as the topography and morphology. Propagationloss models are well known and can be used to estimate the propagationin the coverage area using a propagation loss model for similartopography and morphology. For example, the Lee-New York City, and theHata-Large City models empirically characterize path loss for differentterrain configurations. The Lee model is more popular in the wirelessindustry, while the Rata model is considered more stringent and isgenerally considered as a “worst case” scenario.

Propagation loss models are typically used during the design ofmobile-appliance communication networks to determine thepre-installation location of the base stations necessary to providecommunication coverage in a given area.

FIG. 2 is a block diagram of the steps of one of the preferredembodiments of the present disclosure. The determination of the positionof mobile-appliance location determining sensors begins with adetermination of the base station capabilities 200 including thegeographic location of the base station, the height of the base station,the number of sectors, the orientation of the sectors, the powermanagement and antenna characteristics. Information about theenvironment of the coverage area such as topology and morphology iscollected and an appropriate propagation loss model is selected based onthe environment. Using the appropriate propagation loss model, thesignal propagation characteristics for the signal paths between thepossible locations of the mobile-appliance and the surrounding basestations can be estimated 210.

Based on the wireless air interface being used by the mobile applianceand the associated transmit power management architecture and thedistance between the mobile-appliance and the assumed serving basestation, estimates of the transmit power of the mobile-appliance aremade for various locations in the coverage area where the mobileappliance may reside 220. In one embodiment, this is accomplished bydefining a set of points that span the coverage area in grid likefashion having separations between spanning points on the order of100-500 meters.

Mobile-appliance transmit power affects position accuracy. Locationsystem accuracy improves with the inclusion of data from additional basestations. The ability of additional base stations that may be severalcells away from the mobile-appliance to receive the signal is dependenton the power level of the mobile appliance. Mobile-appliances that arelocated close to its controlling base station are powered down, limitingthe number of distant base stations that can participate in thepositioning. Applicant's disclosure takes into account the effects oftransmit power control architecture.

The received signal strength is estimated 230 for each of the basestations in the vicinity of the mobile-appliance for each of thespanning points in the coverage area based on the estimated propagationcharacteristics, the estimated mobile transmit power and the basestation capabilities. The base stations which are estimated to receive asignal of sufficient strength are identified and p:3fticipate indetermining a location determining accuracy.

For the base stations that have a sufficient received signal strength,TDOA, AOA and collateral data generated errors are estimated 240 foreach of the spanning points. The process of estimating the TDOA, AOA,and collateral data generated errors takes into account the effects ofthe topology, morphology and base station capability that are specificto the processing capability of the location determining sensors. In oneembodiment, three different capabilities are available:

-   -   (a) two-channel TDOA sensor;    -   (b) four-channel TDOA sensor; and    -   (c) four-channel TDOA in combination with AOA sensor.

The channel counts refer to the number of RF channel antenna feeds thatare simultaneously received by the units that make time/angle of arrivalmeasurements. The higher the number of channels, the more accurate thesensor, which comes with a higher cost as well. The processing andalgorithms used to estimate errors and position accuracy during theplanning of a geolocation system are similar to the processing andalgorithms actually used by the geolocation systems to determine thelocation of the mobile appliance.

Collateral data generated errors can be estimated based on theavailability of collateral data for a given spanning point. For example,collateral data may include a series of highway segments located in thesignal coverage area. The highway segments can be used to increase theaccuracy of the location determination of a mobile-appliance located onthe highway. Spanning points located in close proximity to the highwaywould have smaller estimated collateral data generated errors thanspanning points located further from the highway. Thus, a collateraldata generated error can be estimated based on the availability ofcollateral data in the coverage area.

A location determining accuracy can be estimated for each of thespanning points based on the estimated TDOA/AOA errors 250. Thus foreach type of sensor capability the location accuracy is estimated. Theseaccuracy estimations for each of the spanning points can be displayed ona geographic plot as accuracy contour lines 260. The selection of thetype of sensor and the positioning of that sensor can then be determinedusing the estimated accuracy results.

In one embodiment, the location accuracy is estimated using the lowestcost sensor (two channel TDOA) for the entire coverage area. Theaccuracy results can then be displayed as a contour line where theaccuracy is greater than some predetermined threshold. For example, FIG.4 illustrates the estimated accuracy plotted as accuracy contours on ageographic plot of a coverage area where two-channel TDOA sensors areused. The shaded area defined by the contour line marked “125”represents where the estimated location determination error will exceed125 meters 67% of the time. The contour line marked “50” represents anarea in which the location determination error will be less than 50meters 67% of the time.

Based on the accuracies achieved with different sensor capabilities, thetype of sensor with the lowest cost that meets the market accuracyrequirement is selected for that base station site. Additionally, inareas where the predetermined accuracy is met by the lowest cost variant(two-channel TDOA) with margin, some of the location determining sensorsmay be completely eliminated from selected base station sites as long asminimum accuracy compliance is maintained.

In one embodiment of applicant's disclosure, three types of sensorcapabilities can address three broad target market environmentconditions that are common to RF propagation and base station layout orgeometry. With reference to FIG. 3, a continuum of RF environments isillustrated beginning with rural environments, progressing throughsuburban environments, and ending with urban environments. Beginningwith RF environments and cell site layouts found in suburban areas,generally there are relatively good line of site paths from themobile-appliance to the base stations. There typically are a largenumber of base stations that can receive the mobile appliancetransmission and thus make measurements on the RF signal and participatein the location determination. Thus, the suburban environment can beaddressed with two-channel TDOA sensors.

In rural environments, base station sites tend to be sparsely deployed.Thus the site location geometry is relatively poor, and the number ofsites that can receive a mobile transmission appliance is typically low.In these instances, AOA capability needs to be available. This increasedcapability allows a mobile-appliance to be located with only twosensors.

In urban environments, there is a high likelihood that the line of sightsignal path is blocked to many base station sites. Using RF measurementsheavily weighted by multi-path propagation induces high position error.In these cases, four-channel TDOA sensors are used so that spatialfiltering can be done on the RF signal to isolate the direct andmulti-path paths to mitigate the effects of the multi-path on theposition estimates.

Thus, the basic two-channel IDOA unit can be augmented with additionalcapability to address more challenging environments either with respectto propagation (loss of line of sight/high multi-path), or poor basestation geometry. Because the increased capability comes at the price ofhigher equipment costs and higher installation costs, the ability tocreate accurate position error estimates enables an optimization of thedeployment of the location determining sensors to provide the desiredaccuracy at the least cost.

In another embodiment of applicant's disclosure, it may be desirable tominimize the number of sensors deployed in a geolocation system. Forexample, in some geographic areas the installation of the geolocationequipment may be limited or restricted due to practical considerationssuch as political issues, ownership issues, environmental issues, etc.Thus a system having fewer sensors may be more quickly or efficientlydeployed than a system having more sensors. The present disclosure maybe used, in this instance, to select the use of a four channel TDOA withAOA sensor to eliminate the need for three two-channel IDOA sensors,while still meeting the prescribed positioning accuracy requirements.

In another embodiment of applicant's disclosure, it may be desirable tolimit the deployment of the sensors to a specific capability and at alocation other than a base station. For example, an AOA sensor requiresan antenna capable of providing signals for determining the angle ofarrival of the received signal. However, it may not desirable to add anAOA capable antenna to the geolocation system due to client preferences,practical considerations, environmental constraints, etc. The presentdisclosure may be used, in this instance, to select the use of twotwo-channel TDOA sensors at non-base station locations instead of an AOAsensor at a base station, while still meeting the prescribed positioningaccuracy requirements.

Additionally, the prescribed positioning accuracy requirements forspecific applications may vary. For example, the positioning accuracyfor providing turn-by-turn driving directions may be greater than theaccuracy required for providing concierge services. The presentdisclosure can be used to achieve a particular level of accuracy orminimum accuracy for specific applications.

Further, the present disclosure can be used to “upgrade” the geolocationsystems as sensors having increased capabilities are developed andintroduced into the system, or as prescribed position accuracyrequirements are changed.

Thus, applicant's disclosure provides a location determining systemaccuracy assessment to aid in the design, and pre-installation siteassessment and performance analysis for a mobile-appliance locationdetermining system. Note that the accuracy determination and assessmentare accomplished entirely through simulation without the necessity ofmeasuring the actual communication signals, resulting in an efficient,less costly and less labor intensive method of planning a locationdetermining system.

While preferred embodiments of the present invention have beendescribed, it is to be understood that the embodiments described areillustrative only and the scope of the invention is to be defined solelyby the appended claims when accorded a full range of equivalents, manyvariations and modifications naturally occurring to those skilled in theart from a perusal hereof.

1-17. (canceled)
 18. In a mobile-appliance communication system withplural base stations, a method of positioning location sensors fordetermining the location of a mobile-appliance within a predeterminedaccuracy, the improvement comprising the steps of: positioning thelocation determining sensors at some but not all of the plural basestations based on an estimated accuracy of the location calculated bythe location determining sensors; and positioning the locationdetermining sensors at some but not all of the plural base stationsbased on the costs of the location determination sensors.
 19. In amobile-appliance communication system with plural base stations defininga signal coverage area, a method of positioning location sensors fordetermining the location of a mobile-appliance within a predeterminedaccuracy, the improvement comprising the step of positioning thelocation determining sensors based on minimizing the number of sensorsrequired for the coverage area.
 20. The method of claim 19, wherein thelocation determining sensors are positioned as a function of a selectedcapability of the sensor.
 21. (canceled)
 22. In a mobile-appliancecommunication system with plural base stations defining a signalcoverage area, a method of positioning location sensors for determiningthe location of a mobile-appliance within a predetermined accuracy, theimprovement comprising the step of positioning the location determiningsensors at some but not all of the plural base stations based on anestimated accuracy of the location calculated by the locationdetermining sensors.